The invention relates to a method for producing molybdenum trioxide (MoO.sub.3) from raw materials that contain molybdenum disulfide (MoS.sub.2).
The most important raw material for the production of molybdenum trioxide is a floatation concentrate that contains MoS.sub.2 which is often produced as a by-product of copper production in the processing of ores. Such molybdenum concentrates that contain MoS.sub.2 typically contain about 45-55% Mo, 1-5% Cu, 1-5% Fe, and 8-38% S as their main constituents, along with other admixtures as well as matrix constituents. The processing industry requires a molybdenum trioxide having at least 63% Mo, a maximum of 0.3% Cu, a maximum of 0.1% Fe and a maximum of 0.1% S. In known methods for acquiring the necessary products, the sulfidic molybdenum concentrate is calcined in a pyrometallurgical process to melt it and to volatilize the molybdenum trioxide due to the high vapor pressure at low temperatures. Also in known processes, the molybdenum trioxide acquired in this fashion is subsequently washed with water after its condensation out of the exhaust gas in solid form, since volatilized impurities or impurities such as copper and iron discharged together with the molybdenum trioxide are present as sulfates that are easily soluble in water.
In order to obtain a somewhat high proportion of volatilized molybdenum trioxide in the pyrometallurgical process, adequately high temperatures above 1,000.degree. C. must be present when volatilizing molybdenum trioxide as shown in German published application 36 15 437. Only about 60% of the molybdenum content utilized can be volatilized in this way, i.e. a melt/slag is formed in addition to the MoO.sub.3 vapor phase and this melt/slag contains not only the matrix and the main quantity of the metallic impurities of the concentrate, but also contains a high proportion of molybdenum that can amount to about 40%, for example. In previous methods, this slag had to be subjected to a separate after-treatment and metallurgical re-processing that usually involved grinding the cold slag and a subsequent, wet-metallurgical process, see the textbook "Chemische Technologie" by Professor Winnacker, Professor Kuechler, Carl Hanser, Verlag, Munich 1961, Page 466. These many different process steps required to achieve a high molybdenum yield of, for example, 97% and an adequate quality of the MoO.sub.3 as well in MoO.sub.3 cause high losses, entail high production costs and involve a discontinuous operation. The existing process is thus uneconomical overall.
An object of the invention is to create an economical method for the production of MoO.sub.3 from raw materials that contain MoS.sub.2 that, in a compact system, enables a high yield of high-purity molybdenum of greater than 97%, enables a reduction of the various process steps to a minimum degree and also enables a fully continuous process.